This invention relates to an electronically scanned non-rotating cylindrical Tacan antenna and more particularly to a method of producing the required 135 Hz modulation component.
All operational Tacan antenna designs fabricated and tested to date can be described by the principles set forth in "General Design Considerations for Tacan Transponder Antennas" by E. G. Parker and A. Casabona, 1957 IRE Wescon Convention Record, Volume 2, Pages 91-98. The theory presented therein applies to the special case where all primary and secondary radiating sources within the Tacan antenna are omnidirectional in a horizontal plane. While the above article was directed at the design of mechanically rotating antennas, the theory has been extended to include open arrays of fixed radiators fed and phased with either digital or analog scan. These principles have been embodied in an electronically scanned non-rotating Tacan antenna described in U.S. Pat. No. 3,560,978, which describes an antenna having a central radiator, a first plurality of radiators located concentrically around the radiator for producing the required 15 Hz modulation and a second plurality of radiators located concentrically around the first plurality of radiators and along the periphery of the base of the antenna for producing the required 135 Hz modulation component. This has the disadvantage, however, that a desired vertical pattern shaping cannot be obtained.